502 : 
plankton production (1.75 and 8.26 em.’ per m.*), The produc- 
tivity of the lake full of submerged vegetation, is, it seems, less 
than that of one free from it, whether measured in cubic centi- 
meters of plankton or returns for marketable fish. 
The data here presented concerning the inimical effect of 
submerged non-rooted vegetation upon the plankton suggest 
an interesting subject for field or laboratory experiment. In- 
deed, experimental proof is desirable for the generalization ~ 
here advanced. How far it will find support in the examina- 
tion of other localities remains to be seen, for no investigation 
bearing upon the question seems to have been made elsewhere. 
It should be noted that it is not maintained that all vegetation 
is inimical to the development of the plankton, but only such 
as successfully competes with the phytoplankton for the availa- 
ble plant food, and thus brings by its decay no additional 
sources for plant nutrition into the water. These conditions 
are approximately realized where the submerged non-rooted 
type of vegetation prevails. Where, however, by reason of the 
local conditions or the nature of the constituent plants, the 
aquatic vegetation adds by its decay to the fertility of the 
water owing to its utilization of sources of food in the soil 
and the air not available to the phytoplankton, we may expect 
to find the development of the plankton fostered by such vege- 
tation. These conditions are realized wherever rooted, and 
especially emergent, vegetation prevails and contributes by its 
decay to the enrichment of the water. A belt of littoral vege- 
tation of this sort may thus be of considerable effect in main- 
taining the plankton in a body of water. 
INTERNAL FACTORS AND PLANKTON PRODUCTION. 
Under this head attention will be called to certain phases 
of plankton production with which in the present state of our 
knowledge no environmental factors stand in apparent corre- 
lation. From this point of view, which lays emphasis upon the 
reacting organism rather than upon the stimulating environ- 
ment, most of the relations and adaptations of the plankton to 
